(1) Field of the Invention
The present invention relates to the field of read channel electronics for processing the analog signal from thread head of a storage device, such as a magnetic media storage device, and the conversion thereof to digital form.
(2) Prior Art
In a magnetic disk storage system, each disk is organized in tracks and sectors. A track is an annular region of a given radius and a small but finite radial width. A sector, on the other hand, is a portion of a track representing the storage of the smallest unit of user data that the host computer system can access. In general, the disk will contain a large number of concentric tracks, the tracks being as narrow and as closely spaced as possible consistent with the ability to locate and read and write individual tracks without interference with or from adjacent tracks.
In an embedded servo disk drive, the tracks are physically pre-defined at the time of manufacture of the disk drive system by the placement (recording) of signals generally referred to as servo field signals at various positions around each track. Data, on the other hand, is recorded and read between servo fields, the sector data being readable and writeable at the appropriate positions between the servo fields, and a servo field being readable by the same read/write head when the read/write head passes over a pre-recorded servo field. The servo fields are positioned in such a way that the position of the head relative to the center lines of the nearest track can be determined from reading the servo field signals, independent of where the head is between tracks. Also errors in positioning the head on the center of a track can be accurately detected so that corrections in head position may be quickly made.
The general layout of a typical disk is shown schematically in FIG. 1. This Figure illustrates eight servo field regions 20, each in a respective thin pie-shaped region on the disk. More typically, the actual number may be on the order of approximately 50. By way of a specific example, if 48 servo field regions are used, the beginning of the next servo field region will occur 7.5.degree. after the previous one begins, so that head position corrections on a track may be made every 7.5.degree. of rotation of the disk. Still, even with such a large number of servo field regions, only a small percentage of the disk area is devoted thereto, most of the rest being available for the storage of sector information, data, and error detection and correction information.
Prior art computer systems ranging from desk-top computers on up typically would maintain the disk drive system fully operational whenever the computer was on. With the advent of battery-powered lap-top computers and the like, the available battery energy is limited, and accordingly some prior art battery-operated computers can be set to only start the disk drive when a disk operation was called for, and if not followed within a given length of time by another disk operation, to automatically shut down the entire disk drive to preserve power. In the present invention however, the ability of the read channel electronics to turn on and stabilize very quickly in accordance with certain aspects of the invention allows the same to be partially powered down between servo fields to save energy, in spite of the fact that the servo fields are typically only a fraction of a millisecond apart. This, together with the continual reduction in physical size of disk drives and the corresponding reduction in motor power consumption in spite of steadily increasing drive storage capacities, reduces the power consumption of an operating disk drive when it is not reading, yielding higher performance battery-operated systems as well as non battery-operated systems.